Primary aircraft control surfaces, for example ailerons, flaps, elevators or rudder, are mounted to fixed structures such as wings, vertical or horizontal stabilizers by a series of hinges or joints. It is essential that the links (lugs) in each pivot joint maintain their ability to freely rotate about the joints axis without jamming or freezing (seizing) in order that the control surface which it supports can function as required. The links in each joint may be required to react to axial or radial loads imposed by the control surface aerodynamic loadings. Loadings due to aircraft maneuvers (aerodynamic plus inertial) translate axial thrust forces along the hinge line of the control surface which have to be reacted by the pivots as a side or axial load.
Prior art pivot joints have been constructed with primary as well as secondary or backup load paths. During normal operation, however, some of the load is placed upon the alternate or secondary load path even though the primary load members are intact and performing their normal functions.
The prestressing of the members providing secondary or redundant load path while the primary members are in operation is undesirable. The reason for this undesirability is that no guarantee can be made that if the primary member fails that the secondary member will be intact to hold the joint together. Prestressing of the secondary member while the primary members are intact may cause the secondary member to fail first, this could lead to total loss of the joint when the primary member fails.